The present invention relates generally to impact dot printers, and, in particular, to reducing the noise produced thereof.
Generally, impact dot printers are designed to print by driving print wires which are built into the print head so that the ends of the print wires impact a sheet of paper through an ink ribbon. However, a drawback that is frequently encountered in such impact dot printers is excess noise emanating from the resulting collision of the print wires with the sheet of paper. Such noise leaks out of the printer from the sheet discharge section, thereby ultimately increasing the noise level of the printer.
Japanese Utility Model Unexamined Publication No. 64-48263 discloses one way in which noise is reduced from such a impact dot printer. The construction thereof is described with reference to FIGS. 1-5.
FIG. 1 depicts the exterior of a typical impact dot printer, with reference numeral 10 designating generally a printer case. Inside printer case 10, although not shown in the figure, is a print head, a platen, and the like. A sheet discharge section above printer case 10 is covered by a first cover 11 and a second cover 12. As shown in FIG. 3, a sheet discharge path 13 for a printed sheet of paper P is formed by first cover 11 and second cover 12.
As shown in FIGS. 2 and 3, inside second cover 12 are reflecting plates 12a for reflecting sound waves and a sheet guide plate 12b for guiding the printed sheet P. Each reflecting plate 12a extends in a direction orthogonal to a sheet forward direction A. The reflecting plates 12a are arranged to partially change the cross-sectional area of sheet discharge path 13, so that by reflecting the sound wave propagated through sheet discharge path 13 by reflecting plates 12a, the noise level can be reduced.
In FIGS. 1-5, sheet guide 14 guides the discharged printed sheet (which can be separate cut sheets or a continuous length of tractor-fed computer paper) after printing thereon. Second cover 12 covers a large portion of the top of sheet guide 14. Sheet guide 14 is mounted so as to be pivotable relative to printer case 10. To print on a cut sheet (not shown), sheet guide 14 is pivoted upwardly as shown in FIG. 4, so that a cut sheet can be supplied to the print section along the plane created by pivoted sheet guide 14. Second cover 12 is also joined to first cover 11 by pivoting support sections 15 (see FIG. 1) for pivoting relative to first cover 11, such that second cover 12 can be pivoted together with sheet guide 14 when sheet guide 14 is pivoted.
The conventional printers employing the structures described above have the following problems.
First, reflecting plates 12a are arranged only on second cover 12, which results in an insufficient noise reduction because reflecting plates 12a are not located sufficiently close to the print head and to the platen, which are the major sources of noise.
Second, reflecting plates 12a and sheet guide plate 12b have the same height, as shown in FIG. 3, frequently causing the front end of a printed sheet to easily jam. This jamming is a frequent problem particularly with narrow sheets of paper. Although a solution to this jamming problem may be to design sheet discharge path 13 so that it has a greater height, by doing so will also increase the noise because the cross-sectional area of sheet discharge path 13 increases.
Third, as shown in FIG. 4, when sheet guide 14 is pivoted to be able to print on a cut sheet, an opening S1 is provided between side plates 11c of first cover 11 and side plates 12c of second cover 12, causing an excessive amount of noise to leak from opening S1. Similarly, as shown in FIG. 5, an opening S2 is provided between the rear edge of a top plate 11d of first cover 11 and a top plate 12d of second cover 12, which also allows noise to leak from such opening S2.
Accordingly, it is desired to provide an improved impact dot printer having a construction which will operate with a reduced noise level.